Have sniff_hosts reuse existing connection to not waste open sockets

elasticsearch/connection_pool.py

@@ -94,6 +94,7 @@ class ConnectionPool(object):
         :arg randomize_hosts: shuffle the list of connections upon arrival to
             avoid dog piling effect across processes
         """
+        self.connection_opts = connections
         self.connections = [c for (c, opts) in connections]
         # PriorityQueue for thread safety and ease of timeout management
         self.dead = PriorityQueue(len(self.connections))

elasticsearch/transport.py

@@ -95,19 +95,30 @@ class Transport(object):
 
     def set_connections(self, hosts):
         """
-        Instantiate all the connections and crate new connection pool to hold them.
+        Instantiate all the connections and crate new connection pool to hold
+        them. Tries to identify unchanged hosts and re-use existing
+        :class:`~elasticsearch.Connection` instances.
 
         :arg hosts: same as `__init__`
         """
         # construct the connections
         def _create_connection(host):
+            # if this is not the initial setup look at the existing connection
+            # options and identify connections that haven't changed and can be
+            # kept around.
+            if hasattr(self, 'connection_pool'):
+                for (connection, old_host) in self.connection_pool.connection_opts:
+                    if old_host == host:
+                        return connection
+
+            # previously unseen params, create new connection
             kwargs = self.kwargs.copy()
             kwargs.update(host)
             return self.connection_class(**kwargs)
-        connections = list(map(_create_connection, hosts))
+        connections = map(_create_connection, hosts)
 
         # pass the hosts dicts to the connection pool to optionally extract parameters from
-        self.connection_pool = self.connection_pool_class(zip(connections, hosts), **self.kwargs)
+        self.connection_pool = self.connection_pool_class(list(zip(connections, hosts)), **self.kwargs)
 
     def get_connection(self, sniffing=False):
         """

test_elasticsearch/test_transport.py

@@ -84,6 +84,14 @@ class TestTransport(TestCase):
         self.assertEquals(1, len(t.connection_pool.connections))
         self.assertEquals('http://1.1.1.1:123', t.get_connection()[0].host)
 
+    def test_sniff_reuses_connection_instances_if_possible(self):
+        t = Transport([{'data': CLUSTER_NODES}, {"host": "1.1.1.1", "port": 123}], connection_class=DummyConnection, randomize_hosts=False)
+        connection = t.connection_pool.connections[1]
+
+        t.sniff_hosts()
+        self.assertEquals(1, len(t.connection_pool.connections))
+        self.assertIs(connection, t.get_connection()[0])
+
     def test_sniff_on_fail_triggers_sniffing_on_fail(self):
         t = Transport([{'exception': ConnectionError('abandon ship')}, {"data": CLUSTER_NODES}],
             connection_class=DummyConnection, sniff_on_connection_fail=True, max_retries=1, randomize_hosts=False)